The document discusses how to achieve unity and coherence in essays. It defines unity as relating all ideas to a single topic, such as only discussing the advantages of a topic rather than both advantages and disadvantages. Coherence is achieved through logical organization and using transition words and phrases to connect sentences and paragraphs. The document provides examples of different organizational structures and types of transition signals and devices that can be used to create coherence, such as pronoun references and repeating key nouns.